1. Field of the Invention
This invention relates to a method of manufacture of a nonwoven fabric made from cellulose and in particular from a solution of cellulose.
2. Discussion of Prior Art
Cellulose fibres and filaments may be produced by spinning a solution of cellulose in an amine oxide solvent which is then leached into water or a dilute solution of aqueous amine oxide, to produce cellulose filaments which can then be cut into staple fibres. The process of extrusion and coagulation is referred to as solvent spinning, and the fibres of solvent spun cellulose so produced are known under the generic name of lyocell.
It is possible to produce smaller decitex fibres below 1.0 dtex by disintegrating staple fibres. However, this is costly and requires a high energy consumption.
The present invention provides a cheap and effective process to produce a nonwoven textile comprising low decitex cellulose fibres.
Accordingly there is provided a method of manufacture of a nonwoven cellulose fabric made from fibres formed by extruding a solution of cellulose through at least one spinning jet and attenuating the extrudate fibre with high velocity gas flow, the attenuated fibre being collected on a surface on which the fibre web is subsequently coagulated.
The term xe2x80x98gasxe2x80x99 is intended to include vapours, such as steam.
The cellulose solution is preferably a solution of cellulose in an amine oxide solvent, typically a tertiary N-amine oxide and in particular N-methylmorphylene-N-oxide (NMMO). The cellulose solution may contain as little as 2% cellulose by weight; however, the solution preferably comprises 4-22% by weight of cellulose, having a degree of polymerisation of 200-5,000, and more typically 400-1,000.
In a preferred embodiment the cellulose solution comprises 15% by weight of cellulose, 10% by weight water and 75% by weight of NMMO, the cellulose having a degree of polymerisation of about 600.
The attenuated fibre-forming microfibres or fibrils are collected onto a surface and are then coagulated (alternatively referred to as being xe2x80x9cregeneratedxe2x80x9d) by means of water, or a dilute aqueous solution of amine oxide containing up to 20% amine oxide in water.
The gas, preferably air or steam, is blown onto the extruded fibres at a velocity of between 250 m.sxe2x88x921 (meters per second) and 500 m.sxe2x88x921 and has a temperature of between 125xc2x0 C. and 155xc2x0 C., preferably about 150xc2x0 C. The lower the cellulose content of the dope, the lower the air temperature that can be used. The air temperature may be reduced to near 100xc2x0 C. with low cellulose content dopes. The gas velocity should be at least 50 times higher than the velocity of the extrudate fibre emerging from the spinning jet, and preferably between 1,000 and 20,000 times said velocity. The air is directed onto the fibre extrudate at a bias angle, preferably of between 15 and 45xc2x0 relative to the longitudinal axis of the extrudate, and more preferably about 30xc2x0. The air jets may also be biased at a second skew angle relative to the spinning jet so that the air jet axes and fibre axis do not intersect, the air jets being tangential to the surface of the fibre extrudate.
Also according to the invention there is provided an apparatus for the manufacture of a nonwoven fabric comprising lyocell fibres, the apparatus comprising a spinning nozzle through which a solution of cellulose is extruded in operation; one or more gas jets adapted to direct a stream of gas into the extrudate to attenuate the extrudate and form fibrils; a support surface adapted to collect the attenuated extrudate; and regeneration means for coagulating the fibrils on the support surface. Preferably the support surface is provided by the curved surface of a drum.
Because the fibrils or fibres are collected on the support surface before regeneration, the fibres in contact with each other can bond together.
Accordingly, the invention also provides a nonwoven lyocell fabric in which the fibres are bonded together without the use of a binder.